Electron beam diagnostic system using computed tomography and an annular sensor

ABSTRACT

A system for analyzing an electron beam including a circular electron beam diagnostic sensor adapted to receive the electron beam, the circular electron beam diagnostic sensor having a central axis; an annular sensor structure operatively connected to the circular electron beam diagnostic sensor, wherein the sensor structure receives the electron beam; a system for sweeping the electron beam radially outward from the central axis of the circular electron beam diagnostic sensor to the annular sensor structure wherein the electron beam is intercepted by the annular sensor structure; and a device for measuring the electron beam that is intercepted by the annular sensor structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is Continuation of application No. 12/917,028filed Nov. 1, 2010, which claims benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Application No. 61/264,187 filed Nov. 24, 2009, thedisclosure of which is hereby incorporated by reference in its entiretyfor all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to analyzing electron beams and moreparticularly to an annular sensor for analyzing electron beams.

2. State of Technology

U.S. Pat. No. 6,300,755 issued Oct. 9, 2001 to John W. Elmer and Alan T.Teruya for an enhanced modified Faraday cup for determination of powerdensity distribution of electrons relates to the measurement of thecurrent density distribution in electron and ion beams, particularly toa modified Faraday cup having radial slits therein to create an image ofthe current density of such beams, and more particularly to an enhancedmodified Faraday cup utilizing two spaced slit disks, one disk havingone slit wider than the other slits, and a ring to help minimize theamount of secondary electrons and ions from being produced. U.S. Pat.No. 6,300,755 provides the following state of technology information:

-   -   The present invention Electron beams are considered to be the        most precise and clean method available for welding thick        sections of materials. Unfortunately, electron beams suffer one        critical deficiency, namely the repeatability of focusing the        beam to a known power density. Without the ability to reliably        reproduce the power distribution in an electron beam, weld        quality cannot be guaranteed. This problem is exacerbated by the        fact the many welds are made over a period of time and with        different welding operators. Further complications arise when        welds are developed on one machine than transferred to a        different machine for production. An electron beam diagnostic        method has been developed that enables the precise        characterization of the power density distribution in high power        electron beams. Such diagnostic method, which utilizes a        modified Faraday cup, is exemplified by U.S. Pat. Nos.        5,382,895, 5,468,966, 5,554,926 and U.S. Pat. No. 5,583,427.        This electron beam diagnostic method has been utilized, for        example, to certify changes in electron beam welders, and is        further described in J. W. Elmer et al, “Tomographic Imaging of        Non-Circular and irregular Electron Beam Power Density        Distributions,” Welding Journal 72 (ii), p. 493-s, 1993; A. T.        Teruya et al, “A System for the Tomographic Determination of the        Power Distribution in Electron Beams”, The Laser and Electron        Beam in Welding, Cutting, and Surface Treatment State-of-the-Art        1991, Bakish Materials Corp., p. 125, 1991; and J. W. Elmer et        al, “Beam Profile Analysis for the C&MS B231 Electron Beam        Welding Machines”, LLNL UCRL-ID-127549, Jun. 12, 1997.    -   The present invention provides an enhancement of the modified        Faraday cup (MFC) diagnostic device utilized in the        above-referenced patents, and specifically provides an        improvement over the MFC of above-referenced U.S. Pat. No.        5,583,427. The enhanced MFC of the present invention improves        the quality of the signal that is measured by the MFC, and thus        improves the accuracy of the power density distribution        measurements. In the MFC of U.S. Pat. No. 5,583,427, the        electron beam is oscillated around a tungsten slit disk which        samples the beam. The sampled beam current is then measured with        an MFC. The MFC of the patent suffers from two problems. First,        a substantial percentage of the electron current passing into        the Faraday cup could be transported as secondary electrons        and/or ions back up to the tungsten slit disk, and therefore        would not be properly accounted for. Second, with repeated use,        the electrical contact between the tungsten slit disk and the        copper heat sink body would degrade. Also, when measuring        non-circular beams with the prior MFC, there was no method to        orient the measured beam profile with respect to the welding        chamber.    -   The present invention overcomes the above-mentioned electron        capture problems by the inclusion of several significant        additions to the MFC, of which includes a second slit disk        located inside the Faraday cup, a ring added in the Faraday cup        below the second slit disk, a beam trap added within the Faraday        cup, an improved ground arrangement for the tungsten slit disk,        and modifying the tungsten slit disk to orient the beam profile        with respect to the welding chamber.

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfailing within the spirit and scope of the invention as defined by theclaims.

The present invention provides a new concept for analyzing electronbeams that uses an annular sensor rather than the multiple radial slitsensor (For example, the 17 radial slit prior art sensor) used inpreviously electron beam diagnostic systems. The annular sensor changesthe geometry by which the electron beam is scanned over the sensor andhas key advantages over the previously invented enhanced modifiedFaraday cup designs. These advantages include: 1) The annular sensor hasno limitations on how many different electron beam profiles can betaken, which increases the resolution of the computer tomographicallyreconstructed electron beam profile, 2) the annular sensor allows thebeam to be swept in a linear fashion rather than in a circular fashionacross the sensor which is easier for many machines perform, 3) the beamcan be analyzed without having to be swept as far away from the centrallocation, which makes the diagnostic smaller and easier to use on mostelectron beam machines, and 4) the design can easily be incorporatedwith a detached heat sink which makes it simpler and easier tomanufacture, particularly when used for higher power applications.

An annular electron beam diagnostic sensor designed in a number of ways,but all embodiments rely on a circular shaped sensor, that can becontinuous or segmented, and is arranged coaxially with the propagationaxis of the electron beam. The basic principal is to sweep the electronbeam over the sensor at a known speed using the standard magneticdeflection coils that are present on all electron beam welders, and onother electron beam devices such as scanning electron microscopes. Asthe beam crosses the sensor, the beam's current is intercepted,generating a current versus time profile of the electron distribution inthe beam. The current in this signal is then measured, using a fastacting data acquisition system, to render a current versus position ofthe electron beam that is integrated along the length of the portion ofthe sensor that is intercepting the beam.

By making the with of the annular sensor small relative to the size ofthe beam, and sampling the data rapidly, an accurate measurement of thebeam's profile can be made. This process is repeated by scanning thebeam at different angles over the sensor while keeping the beam scandirection normal to the tangent of the annular sensor. Each angle givesa different view of the beams profile which can be analyzed using CTmethods to recreate the power density distribution in the beam.

The present invention has use in electron beam welding, electron beamgun design, focusing of high power electron beams, quality control ofelectron beams, high resolution profiling of electron beams,transferring electron beam parameters between machines and facilities.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfailing within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 provides an illustration of a prior art system for analyzingelectron beams to serve as background for the description of the presentinvention.

FIG. 2 is a simplified conceptual drawing of the present invention.

FIG. 3 illustrates one embodiment of the present invention using slottedFaraday cup technology.

FIG. 4 illustrates an enlarged partial of the inner and outer rings andthe slot.

FIG. 5 illustrates another embodiment of an electron beam diagnosticsystem using a solid wire technique.

FIG. 6 is a cross sectional view of the system of FIG. 5.

FIG. 7 is a diagram illustrates the various factors that are used by thebeam controller to generate a computer tomographically constructed beamprofile.

FIGS. 8A-8D illustrates additional embodiments of the present invention.

FIG. 9 illustrates additional details of the annular sensor that uses asegmented slit illustrated in FIGS. 8A-8D.

FIG. 10 illustrates additional details of another version of the annularsensor that used a segmented slit illustrated in FIGS. 8A-8D.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to the drawings, to the following detailed description, and toincorporated materials, detailed information about the invention isprovided including the description of specific embodiments. The detaileddescription serves to explain the principles of the invention. Theinvention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfailing within the spirit and scope of the invention as defined by theclaims.

Electron beam diagnostics have been developed by the Applicants formeasuring the power density of beams used for welding and otherapplications. The fundamental concept behind the recent diagnosticdevices is based on the enhanced modified Faraday cup (EMFC) design. TheEMFC design uses a circular disk with multiple radially oriented slitsto sample the electron beam at different angles as the beam is rotatedin a circular path over the disk. The data acquired from the EMFCdiagnostic is further analyzed using computed tomography (CT) to rendera power density distribution of the electron beam. This data can be usedfor focusing the beam, transferring electron beam parameters betweenmachines and facilities, and quality control. The EMFC diagnostic hasbeen used successfully at a number of institutions to measure beams upto 8 kW in power. Higher power concepts of the diagnostic have beenpatented based on the multiple slit design, but not yet manufactured.All low power, high power, and micro versions of the EMFC rely on theradial slit design, which has some limitations in that the resolution ofthe reconstructed beam is restricted by having a fixed number ofprofiles (typically 17) of the beam. In addition, the design is one thatis complicated to modify in order to handle higher power electron beams,which in some commercial applications, may be as high as 100 kW, andthere is a requirement to circle the beam in a large diameter circle (25mm) over the slits to provide adequate separation between the slits tomeasure defocused beams.

Referring now to the drawings and in particular to FIG. 1, informationabout the prior art system is provided to serve as background for thedescription of the present invention. FIG. 1 is an illustration of theprior art system that includes a refractory metal disc 2 with a seriesof slits 4. The number of slits shown is 17. The number of slits isrestricted by the allowable spacing of the slits. An electron or ionbeam 6 travels in circular path 8 around the disc 2 and as the beam 6crosses the slits 4 a signal is generated. This signal goes to a dataacquisition system where an image of the current density in high or lowpower ion or electron beams is created. The number of data points takenis limited to the spacing of the slots.

The present invention provides a new concept for analyzing an electronbeam. This new concept uses an annular slit as the sensor rather thanthe disc with slits as illustrated in the prior art. The annular sensorchanges the geometry by which the electron beam is scanned over thesensor and has several key advantages over the prior art design. Theannular sensor has no limitations on how many different electron beamprofiles can be taken, which increases the resolution of thetomographically reconstructed electron beam profile. The annular sensorallows the beam to be swept in a linear fashion (illustrated anddescribed in FIG. 7) rather than the circular fashion across the sensorthis being easier for many machines to perform. The beam can be analyzedwithout having to be swept as far from the beams central location, whichmakes the diagnostic smaller and easier to use on most electron beammachines. This design can easily be incorporated with a detached heatsink which will be simpler and easier to manufacture, particularly whenused for high power applications.

The present invention provides a new concept for analyzing electronbeams that uses an annular sensor rather than the multiple radial slitsensor used in the EMFC. The advantages of the annular sensor are: 1) ithas no limitations on how many different electron beam profiles can betaken, which increases the resolution of the CT reconstructed electronbeam profile, 2) the annular sensor allows the beam to be swept in alinear fashion rather than in a circular fashion across the sensor whichis easier for many machines perform, 3) the beam can be analyzed withouthaving to be swept as far away from the central location, which makesthe diagnostic smaller and easier to use on most electron beam machines,and 4) the design can easily be incorporated with a detached heat sinkwhich makes it simpler and easier to manufacture, particularly when usedin higher power applications. The annular sensor will acquire beamprofile data very similar to that acquired by the EMFC, allowingexisting CT software and methods to be used reconstruct and analyze theacquired data as done with the EMFC.

The annular electron beam diagnostic sensor can be designed in a numberof ways, but all embodiments rely on a circular shaped sensor, that canbe continuous or segmented, and is arranged coaxially with thepropagation axis of the electron beam. The basic principal is to sweepthe electron beam over the sensor at a known speed using the standardmagnetic deflection coils that are present on all electron beam welders,and on other electron beam devices such as scanning electronmicroscopes. As the beam crosses the sensor, the beams current isintercepted, generating a current versus time profile of the electrondistribution in the beam. The current in this signal is then measured,using a fast acting data acquisition system, to render a current versusposition of the electron beam that is integrated along the length of theportion of the sensor that is intercepting the beam. By making the widthof the annular sensor small relative to the size of the beam, andsampling the data rapidly, an accurate measurement of the beam's profilecan be made. This process is repeated by scanning the beam at differentangles over the sensor while keeping the beam scan direction normal tothe tangent of the annular sensor. Each angle gives a different view ofthe beam's profile which can be analyzed using CT methods to recreatethe power density distribution in the beam, much the same as haspreviously done using the EMFC reconstruction method.

Referring now to FIG. 2, a simplified conceptual drawing of the presentinvention provided. Shown in FIG. 2 is a continuous slit or sensor 14that is separated by an outer ring 10 and an inner ring 12. Also show isa central opening 20. There is an electron beam 16 centered at 20. Themotion of the electron beam 16 will be shown and described in greaterdetail in connection with the description of FIG. 7.

One embodiment of the present invention is illustrated in FIG. 3. Theembodiment illustrated in FIG. 3 is designated generally by thereference numeral 300. The embodiment 300 has an annular slit which thebeam passes through as it is scanned over the slit. The slit is madebetween two high temperature refractory metals such as tungsten, and theportion of the beam passing through the slit is intercepted by a Faradaycup arrangement below the slit. The acquired signal is processed throughthe data acquisition system in the same way as for the solid conductorsensor. The advantage of an annular slit is that it can be designed tohandle higher power densities without having to worry about melting thethin conducting wire of the first arrangement shown in FIG. 3. Thedisadvantages are that the slit-type may be more complicated to designand manufacture than the solid conductor, since it requires the use of aFaraday cup arrangement below the slit, similar to that used in theEMFC.

FIG. 3 provides a cross sectional view of the electron beam diagnosticannular sensor system 300. There is a base plate 32 upon which aremounted the inner ring 12, outer ring 10 and the Faraday cup unit 26.Electrical isolation 30 electrically isolates the Faraday cup unit fromthe other items. The Faraday cup 26 is where the signal or data isgenerated and is connected to the data acquisition system 28. The innerring 12 and outer ring 10 are separately grounded at 34 and 36. There isan electron beam source 22 connected to an electron beam controller 24.The electron beam centerline is 20. The angle of the slot 14 will begoverned by the distance 44 of the electron beam source 22 from the topsurface of the unit 300 and the sweep angle 42. Located within thecentral opening 20 is a beam dump 38, cooling passages 40 may be addedfor higher powered applications.

Referring now to FIG. 4 an enlarged partial of the inner and outer ringsand the slot is illustrated. Some materials that could be used aretungsten for the inner and outer rings 12 and 10 while the materialsurrounding the Faraday cup area might be copper.

FIG. 5 illustrates another embodiment of an electron beam diagnosticsystem using an annular technique. Here the sensor is illustrated as asolid conducting wire concentrically surrounding the center ofpropagation of the electron beam. As the beam crosses the sensor, a fastacting data acquisition system gathers beam current versus time data forthe portion of the beam intercepted by the thin sensor conductor. As thebeam returns to its center position, a second profile from the sameangular location is recorded. The beam is then scanned at a new angle,offset by θ deg, and the process is repeated. Since the sensor iscontinuous, θ, can be made as small as desired, thus allowing thediagnostic to gather as many angles as needed for the desired resolutionof the reconstructed beam.

FIG. 5 shows a housing 46 that surrounds the annular sensor 50. In thiscase the annular sensor 50 is a wire. The annular sensor 50 is shownsupported in four places by non-electrical conducting support pins 48that protrude from the inner wall of housing 46. The sensor 50 is shownconnected to the data acquisition system 28. There is a central opening20 in which a beam dump 38 is located. Also shown are the beam source 22connected to the electron beam controller 24. Two sweeps of the beam 16are shown the two sweeps are separated by some angle theta. The angletheta is controlled by the electron beam controller 28.

FIG. 6 is a cross sectional view of the system of FIG. 5. Here we seethe housing 46 and the non-conducting support pins 48 supporting theannular sensor 50. The annular sensor 50 is shown connected to the dataacquisition system 28. Where the connection passes through the wall ofhousing 46 where electrical isolation 54 has been provided. Again a beamcenter line 20 is shown and a beam sweep angle 42 the sweep anglecontrolled by the electron beam controller 24. A beam dump 38 is shownlocated in the central opening 20 and cooling passages 40 can beincorporated for high energy applications. Housing 46 is grounded at 52.

FIG. 7 illustrates the various factors that are used by the beamcontroller to generate a computer tomographically constructed beamprofile. The annular sensor 50 with some unspecified diameter 58 isshown connected to the data acquisition system 28. The doubled headedarrow 44 is the distance of the electron beam source 22 from the topsurface of the annular sensor 50. The sweep angle is 42 and a number ofsweeps 56 are shown. The angle between the sweeps is represented byTheta. The electron beam controller can make use of all these factors tocompile a very accurate beam profile.

Another concept for the annular sensor of the present invention uses asegmented slit as illustrated in FIGS. 8A-8D. In this version, theannular sensor is segmented and arranged in two circular paths withdifferent diameters. The slits are machined into a high melting pointmaterial such as tungsten, allowing the annular sensor to be fabricatedfrom one piece of material. The two sets of concentric annular segmentsare offset so that the gaps between the segments do not line up, whichinsures that as the beam is scanned over the slits there will always beat least one perfect beam profile that is collected. In terms offabrication this design can be manufactured very much the same asprevious versions of the EMFC diagnostic. This design adapted to be adrop-in replacement for the multiple slit diagnostic used in the EMFC.

Referring now to FIG. 8A a concept of the annular sensor is illustrated.In this design two concentric segmented annular slits are provided. Theslits are machined into a high melting pout material such as tungsten,allowing the annular sensor to be fabricated from one piece of material.The two sets of concentric annular segments are offset so that the gapsbetween the segments do not line up, which insures that as the beam isscanned over the slits there will always be data collected.

FIG. 8A shows a one piece sensor body 67 with the two concentricsegmented slits, the outer slit is labeled 60 and the inner slit islabeled 62. A central opening 20 is also shown. Three beam line scans 16are shown and labeled 16 a, 16 b and 16 c. The scan 16 a is showncrossing the inner slit 62 at the node 66 where data 70 is generated andcrossing the outer slit 60 in the gap area at node 68 where no data 70is generated, this is shown on the graph of FIG. 8B. Scan 16 b is showncrossing both the inner slit 62 and outer slit 60 generating data 70 atboth nodes 66 and 68, this is shown on the graph of FIG. 8C. The thirdscan 16 c is shown crossing the inner slit 62 in the gap are at node 66and crossing the outer slit at node 68 where data 70 is generated andthis is shown on the graph of FIG. 8D.

Referring now to FIG. 9, additional details are provided of the annularsensor that uses a segmented slit illustrated in FIGS. 8A-8D. FIG. 9 isa sectional view of the segmented slit design taken on the cutting plane9-9 of FIG. 8A. Shown here is a top plate 64 that is connected to a ringpiece 74 that in turn is connected to a base plate 32, these items 64,74 and 32 are in electrical contact and are grounded at 34, groundingstraps 72 can be added to insure electrical conductivity between topplate 64 and ring 74. The inner slit 62 and outer slit 60 are shownextending into the sensor body 66. The sensor body 66 is electricallyisolated by the electrical insulators 30. The beam line 16 is showndistorted in order to also show the beam source 22 and beam controller24. Data acquisition system 28 is also shown. A beam dump 38 with orwithout cooling passages 40 is shown in central opening 20. The centralopening 20 can be extended through the base plate 32 and the beam dumpcan be located off the sensor which will lower the heat load on thesensor. This may be a desirable option in higher beam powerapplications.

Referring now to FIG. 10, additional details are provided of anotherversion of the annular sensor that uses a segmented slit illustrated inFIGS. 8A-8D. FIG. 10 is a concept very similar to the one shown in FIG.9. The difference here is that the one piece sensor body 66 of FIG. 9 isnow divided into two separate, electrically isolated sensor bodies 76and 78. Separate data acquisition channels relieve the requirement thatportions of a beam only travel through one slit at a time to avoidmixing of data. Thus the spacing between the inner slit 62 and the outerslit 60 may be reduced. All other items pertaining to the illustratedconcept are the same as those shown on. FIG. 9.

Data Acquisition and Computed Tomography

The above concepts give examples of the basic operation principles foran annular sensor based on a solid conductor, a slit, and asegmented-slit type detector. Each design has certain advantages anddisadvantages relative to each other, but all having the ability toprovide much higher resolution of the reconstructed electron beamprofile relative to the multiple radial slit sensor used in the EMFC.The basic data acquired from each type of sensor is identical, giving aprofile of the beam current distribution which can later bereconstructed using computed tomography. From a CT reconstructionstandpoint, the only difference between the annular sensor and themultiple radial slit detector is the orientation by which the beamcrosses the slit. The annular sensor profiles the beam at an angle 90deg from that of the radial slit detector, which can easily beaccommodated by the existing CT reconstruction software. This allows thepreviously developed CT reconstruction software to be used for analysisof both the radial slit data and the annular slit data.

Diagnostic System Design

The basic principal of the diagnostic system is to acquire electron beamprofiles as the beam is scanned across the sensor, and reconstruct thisdata into a power density distribution of the beam. The profiles consistof beam current versus time waveform, where the beam current is directlyrelated to the number of electrons being intercepted by the detectorover a given period of time defined by the sampling rate of the dataacquisition system. Higher power density beams, or higher power densityportions of a given beam, will produce higher currents in the sensor fora given period of time which produces a larger voltage drop across theknown resistor in the data acquisition system. It is therefore importantto collect as many electrons passing over the sensor as possible, and tonot allow any of the other electrons in the beam that are outside thesensor to be collected.

There are different methods of doing this and for the slit-type sensoris a Faraday cup arrangement such as the one described in EMFC. Thesecond aspect of the diagnostic system is to intercept all of theelectrons not in the sensor region, isolate them, and transport them toa suitable electrical system ground. Since the electrons contain a highamount of kinetic energy, the heat dissipated from the electrons mustalso be transported away from the sensor in order to keep it fromoverheating. Many different possible arrangements can be developed forthe annular sensor(s) to isolate the electrons in the sensor from theother electrons in the surrounding portions of the beam, and totransport both the beam current and heat generated from the beam safelyaway from the sensor.

For each of the annular sensor designs discussed above, the electronbeams will be initiated in the center of the annular sensor, and willreturn to this location after each sweep of the beam. Therefore, thecentral portion of the detector will receive the majority of theelectrons and heat and, because of this, must be connected to anelectrically isolated heat sink. Previous versions of the EMFC used avery efficient integral beam trap that doubled as a Faraday cup in thecenter of the detector to measure the total beam current. Low powerversions consisted of copper and graphite elements to act as the heatsink, higher power versions required water cooling and other methods toprevent the detector from overheating. These same methods can be usedfor the annular sensor design. In addition, it is possible to separatethe heat sink from the sensor, so that the majority of the beam's energyis decoupled from the sensor. This is even more important for theannular sensor design since the majority of the beams current willalways be directed at the center of the diagnostic.

The annular electron beam diagnostic sensor can be designed in a numberof ways, but all embodiments rely on a circular shaped sensor, that canbe continuous or segmented, and is arranged coaxially with thepropagation axis of the electron beam. The basic principal is to sweepthe electron beam over the sensor at a known speed using the standardmagnetic deflection coils that are present on all electron beam welders,and on other electron beam devices such as scanning electronmicroscopes. As the beam crosses the sensor, the beam's current isintercepted, generating a current versus time profile of the electrondistribution in the beam. The current in this signal is then measured,using a fast acting data acquisition system, to render a current versusposition of the electron beam that is integrated along the length of theportion of the sensor that is intercepting the beam. By making the widthof the annular sensor small relative to the size of the beam, andsampling the data rapidly, an accurate measurement of the beam's profilecan be made. This process is repeated by scanning the beam at differentangles over the sensor while keeping the beam scan direction normal tothe tangent of the annular sensor. Each angle gives a different view ofthe beam's profile which can be analyzed using CT methods to recreatethe power density distribution in the beam, much the same as haspreviously done using the EMFC reconstruction method.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

The invention claimed is:
 1. An apparatus for analyzing an electronbeam, wherein the electron beam has a central propagation axis,comprising: an electron beam diagnostic sensor adapted to receive theelectron beam; a continuous or segmented circular sensor structureoperatively connected to said electron beam diagnostic sensor, whereinsaid continuous or segmented circular sensor structure has a sensorstructure central axis that is arranged coaxially with the electron beamcentral propagation axis and wherein said continuous or segmentedcircular sensor structure receives the electron beam; a system forsweeping the electron beam from said sensor structure central axis andthe electron beam central propagation axis to and along said continuousor segmented circular sensor structure wherein the electron beam isintercepted by said continuous or segmented circular sensor structure;and a device for measuring the electron beam that is intercepted by saidcontinuous or segmented circular sensor structure.
 2. The apparatus foranalyzing an electron beam of claim 1 wherein said continuous orsegmented circular sensor structure includes a slit.
 3. The apparatusfor analyzing an electron beam of claim 1 wherein said continuous orsegmented circular sensor structure includes a continuous slit.
 4. Theapparatus for analyzing an electron beam of claim 1 wherein saidcontinuous or segmented circular sensor structure is a segmentedcircular sensor structure.
 5. The apparatus for analyzing an electronbeam of claim 1 wherein said continuous or segmented circular sensorstructure includes a wire.
 6. The apparatus for analyzing an electronbeam of claim 1 wherein said continuous or segmented circular sensorstructure is a continuous circular sensor structure.
 7. An apparatus foranalyzing an electron beam, wherein the electron beam has a centralpropagation axis, comprising: an electron beam diagnostic sensor meansfor receiving the electron beam; a continuous or segmented circularsensor means for receiving the electron beam operatively connected tosaid electron beam diagnostic sensor means, wherein said continuous orsegmented circular sensor means has a sensor means central axis arrangedcoaxially with the electron beam central propagation axis, and whereinsaid continuous or segmented circular sensor means receives the electronbeam; means for sweeping the electron beam relative to said sensor meanscentral axis and the electron beam central propagation axis to and alongsaid continuous or segmented circular sensor means, wherein the electronbeam is intercepted by said continuous or segmented circular sensormeans, and means for measuring the electron beam that is intercepted bysaid continuous or segmented circular sensor means.
 8. The apparatus foranalyzing an electron beam of claim 7 wherein said continuous orsegmented circular sensor means includes a slit.
 9. The apparatus foranalyzing an electron beam of claim 7 wherein said continuous orsegmented circular sensor means includes a continuous slit.
 10. Theapparatus for analyzing an electron beam of claim 7 wherein saidcontinuous or segmented circular sensor means is a segmented circularsensor means.
 11. The apparatus for analyzing an electron beam of claim7 wherein said continuous or segmented circular sensor means includes awire.
 12. The apparatus for analyzing an electron beam of claim 7wherein said continuous or segmented circular sensor means is acontinuous circular sensor means.
 13. A method of analyzing an electronbeam, wherein the electron beam has a central propagation axis,comprising the steps of: providing an electron beam diagnostic sensoradapted to receive the electron beam; providing a continuous orsegmented circular sensor structure operatively connected to saidelectron beam diagnostic sensor, wherein said continuous or segmentedcircular sensor structure has a sensor structure central axis that isarranged coaxially with the electron beam central propagation axis andwherein said continuous or segmented circular sensor structure receivesthe electron beam; sweeping the electron beam radially outward from saidcentral axis of said electron beam diagnostic sensor to said continuousor segmented circular sensor structure wherein the electron beam isintercepted by said continuous or segmented circular sensor structure;sweeping the electron beam along said continuous or segmented circularsensor structure; and measuring the electron beam.
 14. The method ofanalyzing an electron beam of claim 13 wherein said continuous orsegmented circular sensor structure that receives the electron beamrenders a current versus position of the electron beam and wherein saidstep of measuring the electron beam generates a current versus timeprofile of the electron beam.
 15. The method of analyzing an electronbeam of claim 13 wherein said step of measuring the electron beamcomprises using a fast acting data acquisition system to render acurrent versus position of the electron beam that is integrated alongthe length of the portion of the sensor that is intercepting the beam.